1. Field-of the Invention
The present invention relates to a self-locking fastener and, more particularly, to a panel fastener which includes positive locking, a holdout device for holding the fastener in a retracted position when the fastener is disengaged and a device for visually indicating to an observer whether the fastener is locked.
2. Description of the Prior Art
Various machines such as aircraft, missiles, etc., which produce, or are subject to, vibration use removable panels sometimes called access panels. These panels are secured by fasteners to various members of the aircraft structure such as the frame and are removable to provide access to electronic, hydraulic, or other types of equipment. As these panels must be removed from time to time, the fasteners therefore must be fast acting. Typically threaded fasteners which include a stud and a nut are used.
A primary problem with threaded fasteners is that the vibration of the panels tends to loosen the stud from the nut. This problem is particularly acute in aircraft as the frequency of the vibration may vary over a wide range.
There have been numerous attempts to overcome this problem. One such attempt involves deforming the nut to a generally elliptical internal cross-sectional shape so that the nut will tightly grip the external threads of the stud to thereby frictionally retard relative rotation between the stud and nut. Because of the substantial amount of friction between the stud and nut, it is very difficult to screw and unscrew the stud from the nut. The high friction between the stud and nut causes substantial wear on the fastener and, upon repeated usage, the gripping capability of the nut is reduced thereby correspondingly increasing the danger that the fastener will become unfastened. Finally, this arrangement does not provide a positive lock, but merely provides a retarding or braking action against rotation of the stud relative to the nut.
The fastener disclosed in U.S. Pat. No. 3,404,716 to Cosenza discloses a positive self-locking feature which locks the stud against counterrotation relative to the nut. The positive lock can be completely disengaged to allow relative counterrotation between the stud and nut. With the lock disengaged, there is no wear thereon as the stud and nut are rotated relative to each other, nor can the lock retard such relative rotation. The Cosenza fastener carries a movable actuator member in the stud. The actuator member is exposed so that it can be moved relative to the stud. The positive lock is responsive to movement of the actuator member to become disengaged from either the stud or the nut to allow relative rotation in both directions between the stud and nut.
An outer end of the actuator member at the head portion of the stud is exposed so that the actuator member is engageable and depressible by the tool which is utilized to rotate the stud. The locking means, are made releasable or disengageable from the stud in response to the depressing of the actuator member. In this manner, the lock is automatically disengaged when the tool for rotating the stud is drivingly engaged with the stud. The locking means is embodied in a pair of locking members the first of which is rotatable with the stud and the second of which is movable axially and held against rotation. When the locking members are held in locking engagement, a positive locking connection is formed between the stud and the second locking member. The actuating member is movable to disconnect or break this locking connection at the will of the operator to allow free rotational movement of the stud relative to the nut without interference from the locking members.
To facilitate indexing of the locking members, each of the locking members preferably includes a ratchet. To provide a positive lock each of the ratchets has a plurality of teeth, the profile of which defines at least one generally axially extending face. The axially extending faces of the two ratchets are engageable so that no rotational forces applied to the second ratchet by the first ratchet through the axial faces will be operative to cam the second ratchet axially. In this manner, the stud is positively locked against counterrotation relative to the nut when the two ratchets are held in driving engagement with each other.
U.S. Pat. No. 4,191,236 to Duran discloses a panel fastener assembly comprising a stud assembly and receptacle assembly for receiving the stud component of the stud assembly. The stud and receptacle of the receptacle assembly include mating locking teeth and a movable pin permitting the teeth to be locked together or disengaged.
Although the fasteners disclosed in the Cosenza and Duran patents improved over the pre-existing fasteners, neither provided a stud holdout capability or a visual indication to an operator that the fastener is properly engaged with the mating receptacle. A panel fastener holdout feature is desirable in that the fastener is held in a retracted position when the fastener is disengaged from its nut member on an aircraft, preventing the fastener from becoming damaged when the panel is removed and moved on a flat hard surface or interfering with the positioning of the panel preparatory to fastening the panel in place. The lack of a visual indication that the fastener is engaged in its positive locking mechanism can lead to safety problems since an operator could be distracted during the fastener insertion, remove the wrenching tool, and thereafter be unable to determine which of the fasteners have been locked in place. This is a particularly serious problem when a large number of fasteners are being installed in a panel. In addition, the actuator member used in the aforementioned Cosenza and Duran patents is always in the same position and thus cannot indicate whether the stud was completely engaged, partially disengaged or totally removed from its mating receptacle. In particular, the position of the actuator member was flush or near flush to the head of the stud, providing no indication to the operator whether the stud was properly engaged.
What is thus desired is to provide a self-locking panel fastener which incorporates a holdout feature and also provides a visual indication to an operator as to whether the fastener is engaged properly with the mating receptacle.